Olau Line was a shipping company that existed between the years 1956 and 1994. It operated a ferry service from the United Kingdom to the Netherlands from 1974 until 1994. Originally based in Denmark, the company passed under ownership of the German TT-Line in 1980.

Olau Line was founded in 1956 by the Danish businessman Ole Lauritzen. Originally the company concentrated in chartering tankers and cargo ships to other shipping companies, but in 1974 Olau Line started a car/passengerferry services from Sheerness in the United Kingdom to Vlissingen in the Netherlands and from Copenhagen (Denmark) to Aalborg (Denmark). The latter line was closed after merely a month of service. Between 1974 and 1976 the consistence of Olau's fleet varied greatly, until in 1976 the company acquired M/S Apollo from Rederi AB Slite and renamed her M/S Olau Kent and chartered M/S Finnpartner from Finnlines, renaming her M/S Olau Finn. These two ships formed the Olau fleet for the next four years.

In 1977 Olau attempted to start a service from Sheerness to Dunkerque, France, but this was not successful. By the end of the 1970s the company was in heavy debt, and in 1979 Ole Lauritzen was forced to sell 50% of Olau Line to the West Germany-based TT-Line. The following year Lauritzen sold his remaining shares of the company to TT-Line. At this time the TT-Line logo was adapted as the new logo for Olau Line, but with red and blue colours instead of TT-Line's yellow and blue. TT-Line decided to invest in new, large state-of-the-art cruiseferries for Olau services. These were delivered in 1981 and 1982 as M/S Olau Hollandia and M/S Olau Britannia, respectively. Unlike Olau's earlier ships, most of which were registered in the United Kingdom, the new ships were registered in TT's homeland Germany.

In the late 1980s TT-Line decided to replace the Olau Hollandia and Olau Britannia with new ships. In 1986 and 1987 the company had taken delivery of two cruiseferries for their route between Germany and Sweden, and it was decided that two additional sisters of the same type would be built for Olau Line. These were delivered in 1989 and 1990, and like their predecessors were also named M/S Olau Hollandia and M/S Olau Britannia.

The new Olau Hollandia and Olau Britannia were more than twice the size of the old ships, and they soon proved to be too large for the route they were built for. Due to high operating costs the ships were taken out of the German ship registry and registered in Luxembourg in January 1993, but action for the German Seamen's Union forced the ships to be re-registered in Germany just a month later. In 1994 TT-Line made plans to move the ships underBahamian flag, but when the German Seamen's Union protested again, TT-Line decided to close down Olau Line in May 1994.

Following the closure of Olau Line the second Olau Hollandia and Olau Britannia were chartered to P&O Ferries, who used them successfully for many years on the Portsmouth—Le Havre service.